The presence of microbial pathogens in water bodies, such as rivers, dams, seawater and swimming pools, where human contact is likely to occur, or, in water intended for human or animal contact and/or consumption, is a potential hazard with the potential to result in illness, disability or even death where these pathogens are inadvertently ingested by humans or animals. Accordingly, there exists a variety of methods for their removal so as to render contaminated water safe for human contact and/or consumption.
Known methods of removing pathogens from contaminated water include mechanical filtration, i.e. physical exclusion based on the size of the microbial pollutants, chemical treatment such as chlorination and ozonation and electrolysis which generates oxidants fatal to the pathogens.
Cryptosporidium can survive up to six months in a moist environment and have been known to contaminate public swimming pools. Several outbreaks of cryptosporidiosis due to contaminated swimming pools have been reported. the contamination is usually due to faecal accidents in the pool and the spread of infection amongst pool users can be rapid. This is partly due to the ineffectiveness of current disinfection procedures. As swimming pools do not normally monitor for Cryptosporidium, awareness of a problem is invariably through incriminating epidemiological evidence. In many cases, cryptosporidiosis manifests as infectious diarrhea with risks of complication in the immunocompromised/immunosuppressed population, for example the very young, the very old, transplant recipients and those undergoing immunotherapy.
In the case of raw water, Cryptosporidium oocysts may be removed by conventional water treatment processes during the production of potable water. These processes involve coagulation with coagulants such as ferric chloride or alum followed by addition of polyelectrolytes as coagulant aids and in some cases high molecular weight polymeric organic filter aids. The coagulated material is removed by either sedimentation or filtration through sand filters.
Water treatment processes are not completely reliable for the removal of Cryptosporidium oocysts and in many cases oocysts breakthrough the plant into the reticulation system. Accordingly conventional disinfectants, such as chlorine or ozone, are added to the filtered water prior to reticulation as a precaution in order to destroy some common water borne pathogenic microorganisms that may have broken through the water treatment plant. However, Cryptosporidium oocysts are unaffected by these disinfectants.
In addition, it is always possible that viable microorganisms may be introduced between the water treatment plant and the domestic user. This may occur by sewage infiltration.
Therefore Cryptosporidium oocysts that enter into the reticulation system pose extremely serious public health concerns since no cure exists for cryptosporidiosis.
In addition to potable water, water in swimming pools, spa pools and other recreational waters may contain, Cryptosporidium mainly through faecal contamination introduced by pool users as well as potentially through the potable water used in the swimming pools.
Normally in swimming pools and spas, the water is continuously filtered through sand filters to remove particulate material and disinfected by chlorine addition followed by recirculation. In some instances low concentrations of inorganic coagulants are added to optimise solids removal. However, if Cryptosporidium contamination occurs, removal by filtration or coagulation/filtration through sand filters may not be completely effective. Detection of oocysts results in pool closure for the treatment of the water, for example, by superchlorination at a level of 3-5 mg/L. The efficiency of superchlorination as treatment for deactivating Cryptosporidium not guaranteed. The use of other stronger disinfectants such as ozone, chlorine oxide or mixtures of strong oxidants has also been tested with mixed success.
Thus whilst there are a number of processes well recognised for the treatment of water sources to produce potable water or to treat recreational waters, a significant problem remains in the ability of those processes to produce water, particularly potable water, that complies with strict regulatory requirements in relation to pathogenic microorganism content. Regrettably, conventional water treatment processes have proven unreliable for their removal from water sources.
The present inventors have recognised the critical importance of providing a means by which microorganisms, particularly pathogenic microorganisms, that may remain after conventional water treatment processes may be removed prior to the distribution of the potable water to the end users.